Milk evaporation process and apparatus



Oct. 9, 1951 J CROSS 2,570,213

I MILK EVAPORATION PROCESS AND APPARATUS Filed Dec. 16; 1.946 3Sheets-Sheet 1 .ZEFEHZEF JOSEPH A. CRoss.

Oct. 9, 1951 c oss 2,570,213

MILK EVAPORATION PROCESS AND APPARATUS Filed Dec. 16, 1946 3Sheets-Sheet 2 JOSEPH A. Cnoss.

Oct. 9, 1951 J. A. cRoss MILK EVAPORATION PROCESS AND APPARATUS 3Sheets-Sheet 5 Filed Dec. 16, 1946 JJT/VEJYYEP JOSEPH' A. C0055.

y HZZQ Patented Oct. 9, 1951 APPARATUS Joseph A. Crosa'Westervllle,Ohio, alsignor to Mojonnier Bros. 00., Inc., Chicago, Ill., acorporation of Illinois Application December is, 1946, Serial No.716,581

4 Claims.

This invention relates to methods and apparatus for evaporating milk toa high density under vacuum and below its atmospheric boiling point. r

The invention provides apparatus and a process for rapid evaporation ofthe milk at a temperature range low enough to avoid the substantialalteration or modification of the solids which has heretofore occurredin milk condensing processes which subject the milk to highertemperatures during evaporation. The invention employs a low temperaturerange and a brief evaporation period to preserve as far as possible thenormal flavor and other characteristics of fresh milk, so that when itis reconstituted back to normal density by the addition of water theproduct will resemble fresh milk as closely as possible, in texture andflavor. The invention also is designed to provide an evaporation processyielding the foregoing mentioned advantages and yet characterizedby-such a degree of eniciency and economy as to make the processcommercially practical and desirable.

An outstanding characteristic of the invention is its use of arerrigerating cycle in which a refrigerant gas is compressed and itslatent heat of liquefaction employed to vaporize water from the milk.after which the liquefied refrigerant is cooled and re-evaporated inheat exchange relationship with the water vapor derived from the milk,this latter step effecting the condensation of the water vapor andexerting a high vacuum upon the milk undergoing evaporation. The liquidrefrigerant thus vaporized is recompressed and recycled again throughthe process.

One of the objects of the invention is to provide an evaporation processfor milk at a temperature range below its atmospheric boiling point.

Another object of the invention is to provide an evaporation processutilizing a refrigeration cycle for vaporizing water from the milk andfor condensing the water vapor and avoiding such high temperatures ashave heretofore been used in the evaporation of milk.

Another object is to provide an apparatus caconnected evaporatorsthrough which milk at successively higher densities is recirculated andin which the water vapor is directly separated from the 'milk andevacuated by a condenser.

Other objects and advantages of the invention will be specificallyalluded to hereinafter or will become apparent from a reading of thespecification.

1n the drawings:

Figure 1 is a diagrammatic elevation of an ap paratus by means of whichthe invention may be practiced;

Figure 2 is a sectional view on the line 11-11 of Figure l;

Figure 3 is a sectional view on the line III1II of Figure '1;

Figure 4 is a sectional view on the line IV-IV of Figure 1;

Figure :1 is a sectional view showing a consensor which may be used inthe process; and

Figure 6 is an end view of one of me evaporator units used in theinvention.

itelerrmg iurther to the drawings, the apparatus includes an evaporatorsystem through which the milk hows while being condensed to the desireddensity, a condenser in which the water vapor derived from the milk iscondensed, a compressor 10]. compressing a refrigerant gas which isintroduced into the evaporators for supplying the neat 101 theevaporation of the milk, a condenser and cooler for completing thecondensation of any portion of the refrigerant gas not condensed in theevaporators during heat exchange with the milk, the cooler serving towithdraw excess heat from the condensed hquid refrigerant. The liquidrefrigerant is then introuuced into the water vapor condenser in heatexchange relation with the water vapor, where the liquid refrigerantthere becomes vaporized and is returned to the compressor forreconversion and circulation through the system.

In the apparatus which I have selected to illustrate the invention, thefirst evaporator unit through which the milk flows includes a verticaltube chest I I having a plurality of vertical tubes l2 fixed in theupper tube plate I! and the lower tube plate l4 (Figs. 1 and 2).

The compressed refrigerant gas (the heating medium) is introduced intothe space surrounding the vertical tubes by means of an inlet pipe iiconnected with a common supply pipe it which supplies refrigerant gas tothe other two evaporator units from the pipe l'l leading from acylindrical drum 2| for discharging the, water vapor and unevaporatedmilk which emerge from the upper ends of the tubes. The drum 2| isjoined to a drum 22 of substantially identical construction, the latterbeing associated with the second tube chest 23. An inwardly turnedflange 24 at the right end of the drum 2|, whose circular inner margin25 is projected upon Figure 2, provides a central opening 25 for thewithdrawal through drum 2| of the vapors collected in the drum 22. Thevapor from both of these drums is then evacuated through a vapor duct26. To assist in imparting a centrifugal-motion to the upwardly risingwater vapors and any entrained droplets of milk, I provide an arcuatebaflle 21 extending longitudinally of the drum 2 I, supported atthemargin 25 of, flange 24 at the right end of drum 2| and supported on theleft end wall 24' of drum 2|, thus being positioned to cause thewatervapors and droplets to rise and circulate above the baflle, throwing thedroplets against the wall of the drum and allowing the vapors as theypass over and beyond the edge of the baiiie to escape centrally to thevapor duct 26.

The droplets of milk which then fall from the drum and anymilk'overflowing from the upper ends of tubes I! will enter a conicalsump 28 and pass downwardlythrough the downfiow pipe 29 and enter thechamber 3|] at the bottom of the tube chest I I. In the normal operationof the device the milk will recirculate many times upwardly through thetubes l2 and downwardly through the pipe 29 under the thermosyphonaction promoted by the heat being applied to the milk and further aidedby the water vapor bubbles which form in the milk and rise in the tubesl2.

The milk to be evaporated is introduced into the first evaporator unitas follows. A deaeration tank 3| (see Figure 1) is supplied with milkthrough a pipe 32, by means of a pump or any other suitable means notshown, the milk being allowed to flow downwardly in film formation 1over a spiral channel 33, giving ample opportunity for a vacuum pump 3!of any appropriate design connected by pipe 35 with the top of the tankto evacuate airwhich may be contained in the milk. This preliminaryseparation of air is desirableto prevent foaming of the milk during itsevaporation in the system and also to avoid counter-pressures resultingfrom unseparated air which might accumulate later in the water vaporcondenser. The milk after passing over the spiral channel falls to thebottom of the tank and is withdrawn therefrom by means of the pipe 36and a variable speed or variable output pump 36 of any suitable designand thus may be regulatably supplied to the system and introduced withsufiicient speed to fiow tangentially into the top of the drum 2| afterwhich it then flows down into the sump 28 at the bottom of the drum.

The next adjacent evaporator unit comprising the tube chest 23 and thedrum 22 constitutes the second evaporator stage of the system. Tubechest 23 is identical with tube chest II and its hood 3! is likewiseidentical with the hood 20.

The milk to be evaporated in the second evaporator flows by gravitythereinto by means of a pipe 38 connected with the sump 23 and with thedownflow type or return leg 33 associated with the second evaporatorunit. The holding and fiow capacities of the first unit should be suchthat the amount per unit of time of milk retuming through down leg 29for repeated recirculation through the first unit will be many times theamount per unit of time discharged through pipe 33. The milk enteringfrom pipe 33 by reason of its previous repeated recirculation throughthe first evaporator unit, has already been considerably condensed andflows downwardly through the pipe 33 and thence upwardly through thetubes in the tube chest 23,. and is repeatedly recirculated through thesecond unit.

Compressed refrigerant gas for supplying the heat to this second unit issupplied. by a short pipe positioned as is the pipe II in Figure 2,while the condensed refrigerant is withdrawn from the bottom in a pipepositioned as is the pipe is and connected with the common drawofl pipeI3. I

The milk being recirculated in the first evapora tor unit is of coursethe most dilute, hence the largest amount of evaporation will take placein that evaporator. A somewhat lower rate of evaporation will take placein the second unit, but to facilitate the obtaining of a condensedproduct under efiicient operating conditions, I prefer a difierent typeof evaporator for the third unit. Because the milk flowing through thethird unit is of greater density I prefer to use a falling film type ofevaporator. This unit is shown in .a side elevation in Figure-6 andincludes a tube chest MI containing a plurality of vertical tubes mountsed in tube sheets at their upper and lower ends. I

of standard construction. The vapor separation drum 4| associated withthe tube chest II is connected with its lower end, the water vapors fromthe tubes being conducted into the drum by a curvedhood 42 which tendsto impart a whirling motion to the vapors. A longitudinally ex-, tendingbaiile 43 positioned as shown in Figure 3 and secured in the drum in anysuitable manner serves to prevent the direct flow of the vapors into theoutlet duct 44, causing them to continue a swirling motion, and enablingmilk droplets, if any, entrained with the vapor to slide along the outersurface of the drum and thence drop downwardly into the sump l5.

In order to promote thehighest efiiciency in this falling film unit itis contemplated that the vertical tubes indicated as 48 in Figure 3 willbe covered with a film of milk entirely to their lower ends. Therefore,some of the milk will drop down into thesump 45 and passing downwardlythrough the pipe 41 will be recirculated by means of the pump 43upwardly through the pipe 49 into the space above the top of the tubechest.

Turning now to Figure 4 of the drawings, a partial sectional view of theconstruction at the top of the falling film tube chest is shown. Each ofthese vertical tubes terminates as indicated in the upper tube plate.Within the chamber 5! and extending upwardly 'thereinto and downwardlyinto the tubes 46 I provide the removable open-ended tubes 5|, one foreach of the tubes 48. These removable tubes are supported centrally andvertically by means of spiders such as 52 having three or more legswhich rest on the upper tube sheet. It will be noted that the lower endof each tube II is flared outwardly to cause the mill; which flowsbetween these tubes and the inner surfaces of the tubes 46 to flow as afilm downwardly beyond that point. The tubes 5| are removable forpurposes of cleaning. The milk delivered by the pump 48 is introducedinto the chamber 50 and allowed to accumulate above theupper tube sheet.It is apparent that the depth or the layer of milk above this tube sheetwill determine the hydrostatic pressure of that body of milk and byincreasing or decreasing the depth of this layer or milk the rate 01flow past the flared lower ends of the tubes 5| may be increased ordecreased, thus enabling the operator to cause the tubes 46 to becompletely covered with film but, not excessively. To this end, the pump48 may be provided with a variable speed drive, and a sight glass 53,shown only in Figure '3 may be provided on the sump to assure theoperator that the pump is always primed.

The compressed refrigerant gas, the heating medium, is supplied to theupper end of tube chest 40 by means of the pipe 54 connected with pipe[5, and the condensed'reirigerant is withdrawn from the bottom of thetube chest by means of a pipe 55 and thence flows into the commondraw-off pipe I8 which is connected with the bottoms 01 all threeevaporator units.

The milk is recirculated through the third evaporator unit repeatedly toallow it to be evaporated to the ultimate desired density. A continuousdraw-off of milk at the desired density is obtained through the pipe 56connected with the evacuator pump 51, which also should have a variablespeed or variable output so that the continuous draw-oil may be properlyregulated to harmonize with the rate of feed and the final productdensity desired.

Briefly, the milk continuously enters the first evaporator unit at thetop thereof and is recirculated many times through the first unit beingconsiderably condensed therein. A continuous stream of partiallycondensed milk flows through the pipe 38 from the sump of the firstevaporator unit into the downfiow pipe 39 of the second evaporator unit,wherein the milk is again recirculated and further condensed. This milkfurther condensed also flows continuously from the sump of the secondevaporator unit through a pipe 60 into the downfiow pipe 41 connectedwith the sump of the third evaporator unit. In this last unit, the milkis recirculated and subjected to evaporation until the operator is ableto maintain a continuous draw-oi! through pipe 56 of milk at the desireddensity.

Turning now to the heating medium, a refrigerant gas, which ispreferably Freon 11 or Freon 21, both of which are well knownrefrigerants, is employed in the system. A compressor SI of any suitableor well known design is employed for compressing the gas. The type orcompressor to be employed should be whichever type will operate mostefllciently with whatever refrigerant gas is used. While I mention Freon11 and Freon 21 it should be understood that other refrigerant gaseshaving characteristics suitable for use in this system may be employed.

-If. Freon 11 is employed, it should be compressed to about 61 poundsabsolute pressure, at which pressure it would have a superheatedtemperature of about 162 F. and would condense at about 160 F. in theevaporators and cause water to evaporate from the milk at about 140 F.The compressed gas is intended to flow continuously through the pipe l1into the upper ends of the spaces surrounding'the tubes in the threetube chests heretofore described.

During heat exchange with the milk contained on the insides of. thetubes it is desired that the Freon 11 will largely, ii not-wholly,condense and will be withdrawn from the bottoms of the tube cheststhrough the common pipe IQ for passage through a tubular water cooledcondenser 63 of standard construction and thence through pipe 84 into atubular water cooled cooler 65. The liquefied refrigerant then will flowinto a receiver through the pipe 51 under control of a valve such as thevalve 68 which may be a liquid level controlled valve. Under theseconditions water will evaporate from the milk at about 140 F. and thewater vapor from all three of the evaporator units will be conductedthrough the pipe 26 into the vertical tubular condenser 69. Thiscondenser is of common construction having an upper tube sheet 10 and alower tube sheet .II with a plurality of vertical tubes 12 fixed inthese tube sheets.

As the water vapor has a temperature of about 140 F. and a pressure ofabout 21% pounds absolute pressure, the refrigerant, in order to be ableto condense the water vapor should be cooled to about F. This mayrequire that some of the liquid refrigerant be flashed off into the topof the receiver 66 from which it may be withdrawn through the pipe 13 tothe compressor 6|.

The refrigerant, cooled to about 130 F., is introduced through the pipe14 into the bottom chamber 15 of the condenser 69 and is allowed to flowand boil upwardly through the tubes, the latent heat of evaporation ofthe liquid refrigerant being obtained from the water vapor, condensingthe water vapor at about F. and vaporizing the refrigerant at about 130F. The refrigerant gas is then withdrawn from the top of the condenserthrough the pipe 16 and conducted into the receiver '66 from which it iswithdrawn by the compressor 6|.

The condensed water vapor is evacuated from bottom of the tube cheststhrough the pipe 11 into a tank 18 from which it is evacuated by meansof a pump I9. Non-condensing ejectors of ordinary construction indicatedas 80 and 8| may be employed for ejecting any non-condensible gases suchas air which may have accumulated along with the water vapor. For theejectors a small amount of high pressure steam may be provided. Therefrigerant gas which evolves from the liquid refrigerant in thecondenser 69 will ordinarily have a pressure of about" 39 poundsabsolute pressure, if Freon 11 be used, and after passing through thecompressor 6|, will have a pressure of about 61 pounds absolute.

In order to remove from the refrigerant the excess heat not required inthe system, which consists principally of the heat of compression, andpossibly other heat picked up from the surrounding atmosphere, water issupplied by means of the pump 02 and is circulated through the cooler 65and condenser 63 and discharged through a pipe 83. In order that theamount of cooling shall be just enough to discharge the excess heat, Iprovide a pressure controlled valve 84 which is connected by the pipe 05to 'the underside of a diaphragm in the pressure regulator 05, thisdiaphragm being exposed to the pressure of the compressed gas in theline H. pressure tends to rise in the line I1, more water will be pumpedthrough the cooler 65 by the pump 02 which will get rid of the excessheat which has caused the higher pressure. Thus, the system may beoperated at substantially uniform pressure and temperature conditions,which Hence if the are conducive to the highest efliciency ot a systemof this kind.

An alternative method of ridding the refrigerant or excess heat, orwhich even may be used jointly with the cooler v85, is the condenser 81(Fig. whichmay be substituted for ejector 80, attached to condenser 69,provided water is available at a temperature lower than the water vaporin condenser 69. Such water would be pumped through pipe 88 intocondenser 81 around weir 89, and falling over the weir would mingle withand condense water vapor from condenser 69, the water and condensatebeing discharged through pipe 90 and a barometric leg not shown.

The inflow of water would be controlled by a by diaphragm 92 operativelyconnected with compressed gas line H. The pressure in this line woulddetermine the amount of water vapor which would be condensed by coldwater from outside the system, thus by modifying the heat exchange loadin condenser 69 tending'to main tain uniform heat balance throughout therefrigeration cycle. The regulating valve should be of a type capable ofready adjustment- Freon 21 will be used in the same manner as is theFreon 11 with only such differences in pressure as may be peculiar tothat gas. For example, Freon 21 should be compressed to about 100 poundsabsolute pressure for use in the evaporator, at which pressure it willhave-a saturated temperature of about 160 F. and a superheatedtemperature of about 1620 F. and will condense at about 160 F. in theevaporators. It will cause the water to evaporate'from the milk at about140 F. and the liquefied refrigerant before being used in the watervapor condenser 69 should be cooled to about 130 F. The gas evolvingfrom the liquid Freon 21 which evaporates in this condenser at about 130F. will have a pressure of about pounds absolute. and after passingthrough the compressor will be restored to pounds absolute.

It will be noted that the systemand the method herein described-operatesat different pressures No. 695,644, filed September 9, 1946, and SerialNo. 554,015 filed September 14, 1944, now Patent No. 2,554,138.

While I have shown two evaporators having an upward flow of milk and oneevaporator which provides a falling film flow of milk it should beunderstood that all of the evaporators may be of the first type, thatis, with the upward flow,

if desired, or that there may be more than two evaporators providing forupward flow of milk in combination with one falling film type at the 2end of the system. Also one upward flow and one falling film flow typein the order named may be used. If the milk is to be concentrated to a Iviscous state a falling film evaporator is most efilcient for the finalconcentration stage, but if a viscous concentration is not asked for,the upward flow evaporators may suffice.

For tubular evaporators of either type shown, an economical size tomanufacture and use is one in which-the tubes have a length in theneighborhood of 10 to 12 feet. Where an evaporator 01' such dimensionsand providing for the upward now of milk is used I nnd that thetemperature diflerentlal herein described between the saturatedtemperature of the compressed rerrigerant and the desired evaporatingtemperature for the milk is adequate to cause the milk to boilsubstantially throughout the length or the vertical tubes. Under suchconditions, bubbles of water vapor will be formed throughout the ntireheight of these tubes and rising through the tubes will bring about arapid thermosyphon circulation of the milk. There will therefore be arapid and continuous overnow or milk from the tops of these tunes, someof this milk will merely overflow and fall into the adjoining sump, forexample, the sump 2s shown in Figure 2, while milk droplets carriedalong with the water vapor will be thrown centru'ugaliy around the drumand will fall into th sump, while the water vapor itself will separatefrom the milk and flow into the water vapor outlet pipe 26. hence,evaporators such as H and 23, in addi tion to requiring no pump for therepeated circu.at1on of the milk through their tubes will have a. largeevaporation capacity, and as the interiors or their tubes will beilooued with milk lrom top to bottom, there will be no danger of anymilk drying on the inside surfaces-or the tubes. The exact height atwhich the milk level should be maintained in an evaporator like ll or 3is subject to some variation, in accordance with me rapidity of boiling,but in any case will not be allowedto rise high enough so that any orthe nuid milk will escape through the vapor outlet along with the watervapor. Usually it the milk level in the sumps at the bottom of each drum2| and 22 is maintained Just high enough to cause a continuous overflowinto the outlet pipes 38 and 60, the fluid milk level will be aboutright. There will thus he a constant gravity overflow from the firstsump into the next evaporator and from the final evaporator in theseries of upward now evaporators into the downfiow pipe such as 50leading to the falling film evaporator, if such a falling filmevaporator is used as the last evaporating unit in the system. In such alast unit a liquid level should be maintained that can be observed inthe sight glass 53, thus giving assurance that pump 48 will always bedelivering milk to the top of this mums film evaporator.

While I have shown and described herein a preferred form of theinvention it should bev understood that the invention is not limited tothe precise details of construction or operation herein shown anddescribed, but that the invention is susceptible of considerablemodification without departure from the scope of the invention definedin the following claims.

I claim asmy invention:

1. In an apparatus for concentrating milk under vacuum, a pluralityofupward flow vertical tubular heat exchangers, a vapor separationchamber positioned adjoining the upper end of each said heat exchangerin communication aith the tubes thereof, means for discharging the watervapor from said chambers, means for returning fluid milk from each saidvapor chamber to the bottoms of the tubes whose upper ends communicatewith said vapor chamber for upward passage again through said tubes ofthe same heat exchanger, means for continuous delivery of -a portion oithe milk recirculating 9 through one heat exchanger and its separationchamber to the next adjoining heat exchanger, a refrigerant gascompressor having its compressed gas outlet connected for delivery intothe space in the tube chest surrounding the tubes in each of said heatexchangers and operable for delivering to each said tube chest therefrigerant gas compressed'to such a-"pressure that it is condensable ata temperature sufliciently above the evaporating temperature of the milkto insure boiling of the milk throughout the entire" -height of thetubes in said heat exchangers,

means for withdrawing condensed refrigerant from each heat exchangerand'for cooling the same thereafter, a water vapor tubular condenser,means for delivering the cooled'liquid refrigerant to said condenser forupward flow through the tubes therein, means connecting the spacesurrounding the tubes in said condenser with the vapor separatingchambers to receive water vapor therefrom,- means controlled by thecompressed gas pressure for continuously eliminating from the re-cyclingrefrigerant substantially the amount of heat added thereto by the heatof compression of the refrigerant gas and means for delivering therefrigerant gas evaporated in said condenser to said compressor forreuse in the system.

2. Evaporation apparatus for multi-stage continuous evaporation ofliquids under vacuum comprising a plurality of vertical tubular liquidevaporators connected in series for progressive concentration of theliquid, the last eva orator in the series having means for recirculatingthe partially concentrated liquid from the bottom into the tops of itstubes and for effecting a downward film flow through its tubes,liquidvapor separation means connected with the lower ends of the tubesin said last evaporator, means for continuously evacuating concentratedliquid from said last evaporator, the preceding evaporators in theseries having means for recirculating partially concentrated liquid fromthe upper into the lower ends of their tubes for passage upwardlytherethrough, liquid-vapor separation means connected with the upperends of the tubes of said preceding evaporators, means for continuouslyadvancing partially concentrated liquid from the first and successivelyto and through each evaporator in the series to said last evaporator,means for continuously sunplying fresh liquid to the first evaporator inthe series, a refrigerant gas compressor connected and regulated todeliver compressed gas at a common pressure to the tube chests of allthe evaporators at a tem erature high enough above the evaporatintemperature of the licuid therein to insure boiling of the liquidthroughout substantially the entire height of the tubes in saidpreceding evaporators to effect thermo-syphon recirculation of theliquid through their respective recirculation means. a vapor condenserconnected to the vapor separation means of all the evaporators and meansfor continuously discharging condensate therefrom, means for collectingliquid refri erant from the tube chests of said evaporators and coolingit to lower than i added thereto by the heat of compression of therefrigerant gas.

3; A continuous process for evaporating milk comprising continuouslyfeeding fluid milk into an evaporator system and partially concentratingthe milk in each of a plurality of successive stages of successivelyhigher concentration by flowing the milk through successivelycommunicating but otherwise segregated vertical tubular heat exchangers,causing the milk to recirculate in several of the stages by repeatedlyflowing it upwardly through vertical tubes in-said heat exchangers anddownwardly outside of said heat exchangers, continuously diverting aportion of the milk from the heat exchanger in one stage to the heatexchanger in the next succeeding stage, utilizing as a heating medium ineach of the stages where the milk .flows upwardly through the tubes acompressed refrigerant gas having a saturated temperature sufficientlyhigher than the milk temperature to effect water vapor separation fromthe milk throughout substantially the entire height of the tubes,cooling to a temperature below the water vapor temperature therefrigerant gas which has liquefied during heat exchange with the milkin said heat exchangers, utilizing the cooled liquid refrigerant in heatexchange with the water vapor to condense the latter while vaporizingthe refrigerant, continuously discharging under vacuum the condensedwater vapor from the system, con tinuously discharging concentrated milkfrom the system, recompressing the vaporized refrigerant and re-using itas a heating medium as aforesaid, and continuously under control of thepressure of the compressedv gas, regulating and conducting the coolingof the refrigerant being re-cycled in a manner to eliminate from therefrigerant in the system substantially the amount of heat, which hasbeen added thereto as heat of compression, for maintaining constantoperating pressures and temperatures of the refrigerant in the system.

4. A continuous process for evaporating milk comprising continuouslyfeeding fluid milk 'into an evaporator system and partiallyconcentrating the milk in each of a plurality of successive stages ofsuccessivelv higher concentration by flowing the milk throughsuccessively communicating but otherwise segregated vertical tubularheat exchangers, causing the milk to recirculate in several of thestages by repeatedly flowing it upwardly through vertical tubes in saidheat exchangers and downwardly outside of said heat exchangers,continuously diverting a portion of the milk from the heat exchanger inone stage to the heat exchanger in the next succeeding stage, utilizingas a heating medium in each of the stages where the milk flows upwardlythrough the tubes a compressed refrigerant gas having a saturatedtemperature sufficiently higher than the milk temperature to efiectwater vapor separation from the milk throughout substantially the entireheight of the tubes, cooling to a temperature below the water va ortemperature the refrigerant gas which has liquefied during heat exchangewith the milk in said heat exchangers, utilizing the cooled liquidrefrigerant in heat exchange with the water vapor to condense the latterwhile vaporizing the refrigerant, continuously discharging under vacuumthe condensed water vapor from the-system, continuously dischargingconcentrated milk from the system, recompressing the vaporizedrefrigerant and re-using it as a heating medium as aforesaid, andcontinuously andregulatably 811111111511 and temperatures of therefrigerant in the sys- JOSEPH ALCROSS.

REFERENCES CITED The following references are of record in the tile orthis patent:

UNITED STATES PATENTS Number Name 5 Date 341.669 Lillie May 11, 1886378,843 Lillie Feb. 28, 1888 780,612 Meyer Jan. 24, 1905 Number NumberDunn June 20', 1911 Grosvenor Dec'. 1, 1914 Beyer et all Sept. 14, 1920Monti Aug. 14, 1923 Kopke -1='eb;'3, 1925 .Badger Aug. 2, 1,932, TeetsowSept. 20, 1932 .Henning Aug,- 13,1935 Thefler June 2,1936

FOREIQN PATENTS Country I Date Great Britain Jan. 12, 1905 AustraliaAug. 3, 1933 Sweden Nov, 9, 1923

